The invention relates to a method for controlling a video reflection device for a motion picture camera containing a CCD image sensor and a video electronic mechanism, and to a device for implementing the method.
In order to expose a motion picture film in a motion picture camera, unexposed film is unwound from a film cassette and intermittently moved past a film gate, where the unexposed film goes into the path of rays through a recording lens. During the exposure of the motion picture film, rays are released into the film path, while for the duration of film transportation from one film image to be exposed to the next, the path of rays is covered by means of a shutter. When the next film image has reached the prescribed position in front of the film gate, the rays are again released into the film path for the purpose of exposing the film image in question.
In motion picture cameras with an adjustable rotary shutter, the release and covering of rays in a film path with intermittent film transportation takes place through a rotary shutter that is mechanically or electrically coupled to the film transport mechanism. The rotary shutter has a semi-circular-shaped reflection surface (dark sector) and an opening sector (bright secto). During film transportation, the reflection surface covers the film gate and leads rays from the film pathxe2x80x94because the reflection surface is facing the objectxe2x80x94through one or several ray dividers into an ocular, a video reflection device, and the like. During film transportation, the object can thus be observed through the ocular, recorded through the video reflection device and transmitted to a monitor. When the motion picture film is stationary in front of the film gate, the opening sector, or bright sector of the rotary shutter, releases rays into the recording path for the purpose of exposing the respective film image.
For the purpose of changing the exposure time of the motion picture film when there is a prescribed or variable film transport speed, the adjustable rotary shutter is formed from two coaxial circular sectors which can be adjusted against one another in such a way that the shutter aperture angle is variable. WO 90/08975 for example, disclosed an adjustable rotary shutter for a motion picture camera that consists of a rotary shutter and a shutter adjusting blade that can be adjusted coaxially thereto. The shutter adjusting blade is connected by a drive mechanism to an adjustment motor coupled to the rotary shutter shaft. The rotary shutter shaft is driven by either the main motor of the motion picture camera for the film transport mechanism or by its own drive motor that is electronically coupled to the main motor of the motion picture camera and/or synchronized with the number of revolutions thereof.
Between the shutter adjusting blade and the rotary shutter or the rotary shutter shaft there is a first recording device in the form of an analog or digital angle indicator, that emits a signal corresponding to the position of the shutter adjusting blade in relation to one or more of the rotary shutter and rotary shutter shaft. A second recording device in the form of a light barrier positioned in the region of the rotary shutter measures the opening time of the rotary shutter during operation.
The changing of the shutter aperture angle can be carried out either manually or automatically, or programmed so that the shutter aperture is adapted to respective light ratios, to achieve specific effects or so that the shutter aperture and thus the exposure time of the motion picture film is adapted to the respective film speed.
By adjusting the shutter aperture angle of the adjustable rotary shutter, the amount of light falling onto the motion picture film is varied. However, the reflection surface of the adjustable rotary shutter that refracts rays from the film path into the viewfinder ocular and a video reflection device during film transportation generally has a constant sector angle of 180xc2x0. Therefore, a constant light quantity goes into the viewfinder ocular and to the video reflection device. On the other hand, if there is a change in the shutter aperture angle, for example by 4 shutter stages from 11.75 to 180xc2x0, a variable light quantity reaches the film.
In the case of an unchanged reflection surface of 180xc2x0 sector angle and constant rotation speed of the rotary shutter, in relation to the video reflection device, the video image becomes too light or too dark depending upon the prevailing light ratios. With an adjustment field of the adjustable rotary shutter from an opening angle of 11.75xc2x0 to an opening angle of 180xc2x0, the light quantity reaching the video reflection device changes by 4 shutter stages.
An adaptation of the video image to the respective light ratios may be produced through automatic gain control (AGC). Such automatic adaptation to the respective light ratios is, however, undesirable if the lightness on the video image is to correspond to the lightness on the film, to create equal ratios.
DE 42 11 427 A1 disclosed a method for reducing the lightness shimmer of video images of a video camera directed at the path of rays of a motion picture camera with an adjustable rotary shutter. The number of revolutions and position of the adjustable rotary shutter are registered by a sensor and emitted as a shutter pulse signal, whereby the video camera has a CCD image sensor, an image storage device and a video signal output. With this existing method, the phase displacement between the shutter pulse signal and a video synchronizing signal is recorded. The amplitude of the video signal emitted from the video camera to the image storage device is controlled depending upon the size of the phase displacement between the shutter pulse signal and the video synchronizing signal, and is used as a control signal for the voltage-controlled intensifier of the video camera.
The existing method can be used to solve the problem that occurs when using video cameras with high light sensitivity in video reflection devices of a motion picture camera. The charge of the CCD image sensor is erased with each semi-image selection, resulting in a strong lightness shimmer with a viewfinder image reflection on a motion picture camera. The rotation speed is recorded and the phase position of the adjustable rotary shutter is emitted as a shutter pulse to a control and regulating device. The control and regulating device contains an image storage device, a programmable binary counter, an octal flip-flop and a digital-analog converter. The connection between the shutter pulse and the control pulses of the CCD image sensor of the video reflection device serves to influence the control voltage of the voltage-controlled intensifier of the video reflection device so that amplitude variations that occur with differing motion picture speeds and video frequencies are reduced to a minimum.
The existing control method does not address the problem that occurs when using a video reflection device with a CCD image sensor in a motion picture camera, into which a highly sensitive or less sensitive motion picture film can be loaded, wherein the video signal emitted by the video reflection device is over-modulated or has an amplitude which is too low.
A further problem is that in the case of a change in the shutter aperture angle of the adjustable rotary shutter of the motion picture camera, the light quantity falling onto the motion picture film in the light phase of the shutter sector is inversely proportional to the light quantity falling onto the CCD image sensor in the dark phase of the shutter sector. Exposure differences of up to 4 shutter stages can thereby arise.
Both problems lead independently of one another to a situation whereby the lightness of the film images can deviate considerably from the lightness of the video images. Therefore, the visual impact of a film recording sequence that is reproduced on a video image can deviate considerably from the visual impact that the sequence imparts on the motion picture film.
It is an object of the present invention to create a method for controlling a video reflection device containing a CCD image sensor and a video electronic mechanism, that ensures adaptation of the video image to differing light ratios and/or shutter aperture angles of the adjustable rotary shutter.
The solution according to the invention ensures that in the case of differing light ratios and/or differing shutter aperture angles of the adjustable rotary shutter, a prescribed light quantity corresponding to the film exposure is processed by the video reflection device. In the case of a constant reflection surface of for example 180xc2x0 with a change in the shutter aperture angle for the purpose of changing the exposure time of the motion picture film, the video image can be varied by at least 4 shutter stages and thus be adapted to the exposure of the film image.
Preferably, a shutter logic fixes the time and duration of the charging of the CCD image sensor depending upon the shutter aperture angle in such a way that the exposure time of the CCD image sensor and thus the light quantity taken up is proportional to the film exposure time. This control makes it possible to adapt the exposure ratios of the video reflection device to changes in the film exposure very quickly and with limited technical switching.
In a preferred embodiment of the present invention, the shutter logic controls the substratum voltage of the CCD image sensor so that the CCD image sensor is constantly discharged during the fading-out of rays in the film exposure path.
In an alternate embodiment, the shutter logic controls the substratum voltage of the CCD image sensor so that the CCD image sensor is discharged before it is charged dependent upon the exposure time of the CCD image sensor that is determined by the shutter logic.
With this control of the shutter logic, a change in the film exposure recorded immediately beforehand in the film exposure phase is converted, and equal ratios created, between the charging of the CCD image sensor and the film exposure.
Preferably, the shutter logic connects the video timing frequency to one or more of the shutter aperture angle determined by a first sensor and the position of the adjustable rotary shutter determined by a second sensor.
The shutter logic facilitates control of the charging of the CCD image sensor dependent upon the adjusted or prescribed film exposure of the motion picture camera both in standstill or out of standstill and during the operation of the film transport mechanism.
A device for implementing the above-described method comprises a microprocessor that on the input side is struck with a video timing signal emitted by the video electronic mechanism and with the output of at least one of a sensor recording the shutter aperture angle and a sensor recording the position of the adjustable rotary shutter. The microprocessor is connected on the output side to a timing generator. The timing generator, which is also struck with the video timing signal, controls the CCD image sensor on the output side and emits output signals to a shutter logic. The shutter logic connects these signals and emits a control signal with which the respective stored charge of the CCD image sensor is once again discharged if the shutter aperture angle of the adjustable rotary shutter deviates from a prescribed value. The shutter logic emits the control signal to a component that is subsequently switched and that influences the substratum voltage of the CCD image sensor, whereby the component times the substratum voltage for the purpose of discharging the CCD image sensor.